The present invention relates to a control apparatus for controlling the feed rate and batch size of a material feeder. More particularly, the present invention relates to a control circuit for controlling the armature current to a DC drive motor thereby controlling the operation of the material feeder powered by the drive motor.
Control apparatus for controlling the feed rate and batch size of material feeders are well known in the art. Two such devices are disclosed in U.S. Pat. No. 3,724,720 and U.S. Pat. No. 3,763,943.
The present invention overcomes certain disadvantages of these and other prior art devices by utilizing digital electronic counting techniques for controlling both the feed rate and batch size of a material feeder. The utilization of such techniques in the manner shown herein, provides reliable, fast and efficient delivery of material with extremely high batch size and accuracy.
The apparatus of the present invention comprises a signal generators which continuously monitors the weight of material delivered by a material feeder. As long as the weight of material delivered by the feeder is below a first predetermined value, the signal generators enables a first pulse generator which generates a pulse train having a comparatively high pulse repetition frequency. The pulse train so generated is applied to the input of a motor speed controller which supplies a DC motor powering the material feeder with an armature current proportional to the pulse repetition frequency of the pulse train applied to its input. In the preferred embodiment a feedback loop is provided to assure a constant feed rate despite irregularities in the load on the feeder. When the weight of material delivered by the feeder reaches the first preset value, the first counter means generates a dribble speed signal which disables the first pulse generator and enables a second pulse generator. The second pulse generator generates a pulse train having a pulse repetition frequency substantially less than the pulse repetition frequency of the first pulse train. The second pulse train is applied to the motor speed controller which, due to the lower pulse repetition frequency of the second pulse train, will supply a lower level of armature current to the DC motor thereby causing the feed rate of the material feeder to decrease.
When the weight of material delivered by the feeder is detected to have reached a second preset value, the first counter means will generate an end of batch signal which disables the motor speed controller thereby removing the armature current from the DC motor and discontinuing the delivery of material by the material feeder.
For the purpose of illustrating the invention, there are shown in the drawings forms which are presently preferred; it being understood, however, that this invention is not limited to the precise arrangements and instrumentalities shown.